A phase difference plate is widely used as a component of a display device, such as a liquid crystal display device and an organic electroluminescent (hereinafter sometimes referred to as “organic EL”) display device. A phase difference plate used in the display device may be required to uniformly express a desired phase difference of λ/4, λ/2, or the like over the entire wavelength region for display (usually visible region), thereby exerting the effect over the entire wavelength region for display.
If it is possible that such a phase difference plate as a long-length film having a desired width is continuously manufactured in a manufacturing line and a phase difference plate having a rectangular shape that corresponds to a rectangular display surface of a display device is cut out from the resulting long-length phase difference plate, efficient manufacturing of such a phase difference plate is made possible. Furthermore, if it is possible that the cutting is performed so that sides of the rectangular phase difference plate correspond to directions close to directions parallel to the lengthwise and widthwise directions of the long-length phase difference plate, more efficient manufacturing is made possible.
The phase difference plate in the display device may be required to have a slow axis at a certain angle, such as 15°, 45°, or 75°, relative to a transmission axis of a co-used polarizing plate. For example, when a linear polarizer and a λ/4 wave plate are used in combination to express an anti-reflection function of external light, the phase difference plate is required to have a slow axis at an angle of 45° relative to a transmission axis of the linear polarizer. In many cases, polarization axes of the polarizing plate include a transmission axis in a direction parallel to the longitudinal or lateral side of a rectangular display surface of a display device. In manufacturing of the linear polarizer as a long-length film, a linear polarizer having a transmission axis in a direction parallel or perpendicular to the lengthwise direction, in particular in a direction perpendicular to the lengthwise direction, can be easily manufactured. Therefore, if it is possible that a long-length phase difference plate having a slow axis at a certain angle, such as 15°, 45°, or 75°, relative to the widthwise direction is manufactured, the manufacturing is very advantageous to manufacturing of the phase difference plate for the display device.
As one of methods for obtaining the phase difference plate, a method in which a compound capable of exhibiting a liquid crystal phase is molded into a solid film while the state of exhibiting the liquid crystal phase is kept is known. Specific examples of the method may include a method in which a composition containing a polymerizable liquid crystal compound that is polymerizable and capable of exhibiting a liquid crystal phase is applied onto a surface of an appropriate substrate to form a layer, the polymerizable compound is oriented within the layer, and the polymerizable compound is then polymerized while the oriented state is maintained, to form an optically anisotropic film. According to such a method, a phase difference plate that uniformly expresses a phase difference over the plane can be obtained. When the polymerizable liquid crystal compound is appropriately selected, a phase difference plate that causes a uniform phase difference at a visible light wavelength region can be obtained (for example, Patent Literature 1).
As the method for orienting such a compound capable of exhibiting a liquid crystal phase, a method in which an orientation-regulating force is imparted to a surface of a substrate, a composition containing a compound capable of exhibiting a liquid crystal phase is applied onto the surface and placed under conditions suitable for orientation is generally performed. Examples of the method for imparting an orientation-regulating force to a surface of a substrate may include a method through rubbing (for example, Patent Literatures 2 to 4) and a method through optical orientation (for example, Patent Literatures 5 and 6). In addition, a method of using a film to which an orientation-regulating force is imparted by a stretching treatment as a substrate to orient a liquid crystal compound on the film is known (for example, Patent Literatures 7 to 9).